Minimal gas producing low detonation rate explosive and detonation sources



Jan. 24, 1967 R. w. GATES 3,299,311

MINIMAL GAS PRODUCING LOW DETONATION RATE EXPLOSTVE AND DETONATION SOURCES Filed 001;. 2, 1964 FRACUON RELEASE RATE P/PmOX O I I I I I I I I l TIME period (l/a)lengrhs INVENTOR. ROBERT W GATES A r TORNF Y United States Patent M 3,299,811 MINIMAL GAS PRODUCING LOW DETONATION RATE EXPLOSIVE AND DETONATHON SOURCES Robert W. Gates, Menlo Park, Calii, assignor to the United States of America as represented by the United States Atomic Energy Commission Filed Oct. 2, 1964, Ser. No. 401,281 16 Claims. (Cl. 10224) The present invention relates to explosive compositions and, more particularly, to an explosive composition having a low stable detonation rate and which produces minimal amounts of gaseous reaction products and to sources incorporating such explosive for developing desired energy release profiles.

Explosives, pyrotechnic and propellant compositions hve heretofore been provided to supply heat, explosive energy, propulsion forces, shock forces and other desired effects under a wide variety of conditions and to provide a wide variety of explosive effects. However, compositions heretofore provided are unsuitable, for example, as energy sources for simulating events such as the effect of reactivity excursions in order to determine effects thereof on nuclear reactor containment components. Accurate elevation of possible damage from such as excursion using scale models depends largely upon the degree to which excursion conditions including the rate, amount and duration of energy release are validly simulated. A generalized power-time profile of a nuclear power burst or excursion, thought to be characteristic of the energy release causing explosive damage during a runaway excursion is disclosed in the report Containment Conference at Armour Research Foundation, Chicago, Illinois, May 20 21, 1957 at page 25, and is reproduced hereinafter. The curve is of the exponential form P/P max=e with a time scale such that unit change in time (one period) increases power by a factor of e. The rising and falling portions of the curve are generally mirror images and are separated by an interval of about two periods during which essentially uniform maximum power is generated. Total effective duration of the burst, wherein about 95% of the total energy is released, approximates seven periods. With typical periods ranging from 1 to 50 milliseconds energy burst durations of from 7 to 350 milliseconds are typical and corresponding total excursion energy estimates range between 200 and 4000 M -sec, equivalent to 100 to 2000 lb. of TNT.

Small scale simulation of such an energy release, for example, using a scaling factor of reduces the foregoing duration limits to 0.3 and 15 milliseconds, respectively. The lower end of such range is appreciably larger than the detonation time of most conventional high explosive events, at least for those involving sizes and amounts of explosive consistent with scaled reactor dimensions and energies. Propellant and pyrotechnic materials, heretofore available, having much slower rates of burning than high explosives, lend themselves to the simulation of long duration excursions; however, they have the serious disadvantage that the rate of energy release is strongly affected by variations of confinement pressure in common with the aforesaid high explosives. There accordingly exists a need for a material with a lower detonation velocity which produces low shock pressures, large amounts of solid and liquid products corresponding to those produced from reactor components by an excursion and appropriate uniform, controllable large total energy releases, and most desirably a wide range of detonation velocities and energy yields.

A composition hereinafter termed Calpoke comprising a major proportion of comminuted aluminum metal, a lesser amount of a divalent metal perchlorate and generally smaller amounts of certain high explosive materials 3,299,811 Patented Jan. 24, 1967 has now been discovered which as a high heat of reaction, will ignite in small diameters as well as large diameter tubes, has a low detonation velocity, and produces only small quantities of gaseous reaction products suitable for simulating nuclear reactor source excursions and runaways under a wide range of duration periods and energy releases as well as other relatively long and sustained duration energy release events. Tube sources containing such composition and adaptedto produce desired energy release simulations are also provided.

Accordingly it is an object of the present invention to provide a new and improved explosive of pyrotechnic composition.

Another object of the invention is to provide a low detonation velocity explosive composition which produces minimal amounts of gaseous materials.

Still another object of the invention is to provide an explosive composition having a high heat of reaction, low detonation rate, and produces minimal quantities of gaseous materials suitable for simulating long duration energy release events.

A. further object of the invention is to provide a source device employing a low detonation rate explosive to simulate long duration energy release events.

Other objects and advantages of the invention will become apparent from the following description and accompanying drawings, of which;

FIGURE 1, is a power-time profile of typical nuclear reactor excursions, of which curve A is a generalized profile of such a typical excursion, curve B is a stepped source simulation profile and curve C is a simplified rectangular curve profile produced by a simple tube-low detonation rate explosive source in accordance with the invention; and

FIGURE 2 is a source utilizing a low detonation rate explosive composition for producing nuclear reactor excursion energy releases.

The low detonation rate minimal gas producing explossive composition of the invention, i.e., Calpoke, is generally formulated of 10% to 30% by weight of PETN (Pentaerythritol-tetranitrate), 15-35% by weight of calcium perchlorate and 4060% of comminuted aluminum. Compositions used extensively in simulating nuclear reactor excursions correspond to those in midsections of the aforesaid ranges, i.e., about 20% by weight of PETN, about 25% by weight of calcium perchlorate and about 55% by weight of aluminum which compositions are preferred. Material of the latter composition has a detonation velocity of about 1250 meters/ second and releases about 2500 calories/ gram of material reacted. The principal reaction products of the explosion are solids or liquids at the detonation temperature, e.g., A1 0 and metal chloride such as CaCl Using other admixtures in the ranges set forth above detonation velocities in the range of at least about 1000 to 2000 meters/second and with caloric outputs above and below the above-indicated value can be obtained. Certain other high explosives which can be produced in finely divided forms such as HMX-cyclo 1, 3, 5, 7-tetramethylene 2, 4, 6, S-tetranitramine RDX-cyclo l, 2, S-trimethylene 2, 4, 6-trinitromine, and tetryl-picrylnitromethylamine can be used in a similar fashion to PETN. Compositions formulated of materials having the foregoing properties are appropriate for the simulation of a wide range of long duration explosive events including the simulation of nuclear reactor runaways with a simple rectangular energy release profile such as curve C of FIG- URE 1. Such a profile is produced by a single tube of uniform diameter filled with the composition. Such a source slightly shorter than a model reactor vessel could be used to simulate, e.g., a one millisecond event, providing a simple easily reproducible system for analysis. A stepped source, i.e., variable or stepped diameter sources,

can be used to produce the profile of curve B which more nearly approximates the generalized profile, curve A; however, the use of such a more complicated source configuration possibly cannot be justified since it is not apparent that, for reactor model test purposes, the pressure pulse experienced by the vessel wall is significantly different from that produced by a simple uniform diameter tube source.

For formulating the Calpoke composition PETN or other high explosive mentioned above, in a finely-divided form produced, e.g., by recrystallization is employed. Ignition reliability is improved as the proportions are increased in the range of to (by Wt.) and above and detonation velocity is likewise speeded. The calcium perchlorate is generally ground to a very fine consistency under anhydrous conditions and particle sizes of below about 50 microns and preferably below about 35 microns are used. Aluminum in leaf, flake or platelet form is preferred over spherical, needle-like and like forms since it has been found that such materials, often provided as a paint or surface coating pigment, are reliable, safe and inexpensive. Such a material is far superior, for example, to 7 micron diameter spheroidal particles which produced a composition too sensitive to ignition to permit easy compounding and fabrication. Leaf-like, flake, or platelet form aluminum metal having major dimensions of the order of 100 microns have been found satisfactory in practice. However, such materials with major diameter dimensions as small as about 50 microns and larger, e.g., 200 microns and above should generally prove suitable provided that the thickness is not unduly increased. Increasing the proportions of aluminum above stoichiometric proportions tends to reduce the final reaction temperatures and pressures by sewing as a heat sink.

A quite Wide variety of compositions was investigated in the course of discovering that of the present invention. Initially, compositions containing, by weight, 20% PETN, 48% KClO and 32% and 44% aluminum, respectively (Slowpoke 32), (Slowpoke 44) were found which had a detonation velocity of about 2000 m./sec. and which were believed at first to be suitable to obtain the desired performance. However, damage to test model components was greater than expected or desired. A composition (Slowpoke 56) containing more aluminum, i.e., 56% by weight which therefore contains excess aluminum which tends to lower the reaction temperature produced more favorable pressure and model damage but was too unreliable in smaller grain sizes. Comparative data for various other compositions and that of the invention (Calpoke) are given in Table I which follows.

TABLE I Properties of source materials In view of the differences in fragmentation found to be produced by supposedly identical sources of Pyrocore, Calpoke, and Slowpoke, it became evident that energy output and period were not the only criteria affecting the fragmentation. The actual damage produced is directly caused by the action of pressure upon the vessel wall. Consequently, a series of measurements were made to try to relate the pressure pulse in the vessel to the fragmentation.

A steel pressure bomb was constructed with internal dimensions the same as those of the -scale vessel. Sources of equal energy output and identical periods of the various source materials were detonated in this vessel and attempts were made to measure the pressure produced.

Initially, the transducer used to measure the pressure was a Kistler 601, manufactured by the Kistler Instrument Corp. This gage has a high frequency response and a pressure range of from /2 to 200,000 p.s.i. and low acceleration sensitivity (0.2 p.s.i./g.). The size of the gage was such that it could be fitted into the bomb. The gage appeared to have only one resonance frequency (140 kc.) and it would seem feasible to use it with fair accuracy to a frequency of 30 kc. The transducer element is a quartz crystal which generates an electrical charge proportional to crystal distortion. The measurements are made by determining the voltage this charge generates when placed on a known capacitor. However, for proper response at low frequencies the input impedance must be high. Best results are obtained by using a Kistler amplifier-calibrator with the gage.

The unfiltered pressure traces first obtained from the helical sources were unreadable even though the readings were taken at the center of the base of the bomb to avoid major oscillations and variations. The only repeatable pressure traces were obtained using a 5 kc. low pass filter. The readings obtained with this filter are not representative of the true wave form, and can only be used to provide a relative measure of the performance of the source materials.

This pressure information provides another tool for the examination of source materials with which to extend the working range of the model system. The relatively high detonation velocity of Pyrocore makes it impossible to fabricate the longer period sources. Consequently, it is desirable to have a material with the same energy characteristics as Pyrocore to extend the range so that direct comparisons between the results obtained with the new material and those obtained with Pyrocore are possible. One of the other source materials investigated, i.e., Slowpoke, had all the outward characteristics of Pyrocore but Smallest Detonation Heat oi Diameter Relative Source Material Velocity Reaction successfully Composition Pressure (mm./sec.) (oal./g.) fired Levels (grains/ft.)

MDF 7. 3 1, 440 0.25 100% PETN 0 Pyrocore 1 4. 2 1, 560 4 20% PETN.

Slow-poke 32 2. 0 2, 200 12 Slowpoke 44 1. 43 2, 436 25 Slowpoke 56 1. 35 2, 440 37 Calpoke 1. 25 2, 500 s 1 Values are for 20 grains/it. Pyrocore.

This material is manufactured with different compositions in different core loadings. The composition of the core and consequently its characteristics (litter from core loading to core loading.

produced greater damage to models; other materials, Slowpoke-56 and Calpoke, had the same characteristics but produced comparable model change. An investigation of the relative pressures produced by the alternate materials indicated that the high damage producing Slowpoke produced considerably higher pressure during reaction than the other materials. The results of these tests are listed in Table II below.

TABLE 11 Source material pressure ratios [ALL PRESSURES FROM 5 KC. FILTERED TRACE] Peak Average Simulated Shot No. Material Peak Pressure (p.s.i.)

Pressure Ratio Period (msec.)

PC Pyrocore. SP Slowpoke. 0P Calpoke.

The physical dimensions of the sources that would be required to cover the entire range of simulated reactor events are listed in Table III infra. This shows the lengths required to make sources covering the time periods of major interest, and the core loadings required to cover the energy release range for the listed source materials. table shows that MDF, Pyrocore, and Slowpoke 32 cannot be used for the longer period sources because the lengths involved are much too long to fit into the model vessel. The data also show that Slowpoke 32 and 56 cannot be used for the longer time period sources in the low energy range because the core loading required is less than the core loading of the minimum charge that will sustain detonation. The only material that can be used over the entire range is Calpoke. The versatility of the present composition for use over a wide range of diverse conditions is accordingly demonstrated.

The

produce gas. Both factors cooperate to reduce the production of gaseous products and the undesirable efiects produced by excessive gas pressures on burning rate, etc., which result when perchlorates of monovalent alkali metal, e.g., KCIO are used instead of a perchlorate of a dibasic or higher valency cation, e.g., a divalent alkaline earth metal is used in the perchlorate, e.g., Ca(ClO Certain other divalent metal perchlorates can likewise be employed, e.g., those of alkaline earth metals such as Mg and Ba which due to the composite action mentioned above produce solids or only low vapor pressure amounts of chloride reaction products at explosion temperatures. Perchlorates of trivalent metals such as Al and B would produce lesser molar amounts of reaction product chlorides; however, the vaporization temperature of the chlorides of such materials is generally quite low and genenerally below explosion temperatures so that the bene- TABLE III Comparison 0 plzyszcal dimensions of sources MDF Pyrocoi'e Slowpoke-32 Slowpoke-56 Calpoke Source Energy Period (Mm-sec.) (msee) Length, Load, Length, Load, Length, Load, Length, Load, Length, Load, in. gr./ft. in. gin/ft. in. gr./it. in. Ell/fl in. gr./ft.

1 Too Long or too big for use. 9 Less than Failure Diameter.

7 fits derived from the stoichiometry are offset partially by increased vapor pressures at the reaction temperature. Sources for producing low detonation rate explosions are provided in accordance with the invention as shown in 3 dry nitrogen and transferred to a tumbling barrel blender. The blender was heated to 140 F. and a vacuum of 200,11. pressure was maintained in the blender chamber. These conditions kept the material from absorbing water during FIGURE 2 of the drawings wherein an elongated ductile 5 mixing. The mixing under vacuum was continued for 45 metal tube, e.g., lead or 3% antimonial lead, is employed minutes. The blender was then purged with dry nitrogen as an exterior case. For some purposes plastic or other and a remote operating valve was attached to the blender. tubes can be used as long as the case is impervious to Source tubes 11 were connected to this valve with alength moisture. Normally the tube is of uniform wall thickof tygon tubing and purged with dry nitrogen. The valve ness and interior diameter but the tube may be tapered, was opened remotely and the tube filled with Calpoke. stepped or otherwise shaped to provide desired time-pres- The valve was closed and the tube was removed together sure profiles, etc. An insert plug 12, e.g., of methyl with its connecting length of tygon, and was capped to methacrylate plastic, is employed to cap one end of tube exclude air. The tube was then placed in a =jolter, and 11 which plug is provided with a central opening in which jolted until the Cal oke in the tygon tube had been comis axially disposed electrical detonator 13 (e.g., an M36 15 Pacted into the source tube. The tygon tube was then cap having electrical circuit detonator wires 14. Booster removed and the source tube sealed for use. The tubes pellets, e.g., of tetryl can be used to improve ignition if were weighed before filling and again after filling to check some initial accelerated burning rate can be tolerated. the amount of Calpoke in each tube. Any tubes which Other detonators or detonating lens systems can also be were light or heavy were reprocessed. used. The tube 11 is filled with explosive material 16 by 20 In model tests a simplified reactor model was used which a method described below to uniform density and the retained the basic features of actual reactor structures, i.e., open end thereof is closed with plastic plug 17. Propressure vessel, concrete biological shield and access plug. vision may be made for measuring the longitudinal detona- Physical sizes of reactor cores are such that a sealed (1:24) tion velocity of the source for monitoring purposes by energy source must be contained in a cylindrical volume providing a fine, lightly-insulated resistance wire, e.g., of of 20 cubic inches. A full size reactor vessel 24 feet in about 85 ohms/ft. 18 entering the tube 11 at the end diameter and 42 feet high with three inch thick walls may distal to said detonator and extending in proximity to be sealed at and by vessels of 1 ft., 2 ft. and 4 the inner wall thereof within explosive 16 to be grounded ft. diameter respectively. Sources illustrated in FIG. 11 to the tube 11 at the detonator end. A ground lead 19 and Table IV gave constant velocities of detonation of affixed to tube 11 may be used to complete the monitor- 1260 m./ sec. with no variation as diameter was varied. ing circuit and measurements may be made as disclosed No scaling effects were noted so that such sources could by A. B. Amster, et al. Review of Scientific Instruments, be used reliably and over a very wide range of conditions. 31 188-192 (1960). Dimensions and loadings of the pre- Also, Calpoke detonates at reliable rates without substanferred composition, supra,'f0r three different scale model tial variation from batch to batch, with changes in diameter sources are set forth in Table IV which follows. of changes, change in loading density, and even with varia- TABLE IV Explosive source data A" Dimen- B Dimen- Tube Inner Tube Outer Grams Scale sion, inches sion, inches Diameter, Diameter, Per Tube inches inches Calpoke tel 8% 8% 0.313510. 015 0.375 9.1

The A dimension is the distance between emerging ends of resistance wire 18, and dimension B is the distance between the inside ends of plugs 12 and 17 of the device shown in Figure 2 of the drawing.

The sensitivity of the composition to ignition and safety during compounding and fabrication is not known with certainty so that remote preparation and loading techniques have been used. Moreover, some of the components are hygroscopic, e.g., calcium perchlorade and low melting so that anhydrous conditions must be used and grinding is somewhat difiicult.

The following exemplifies the method compounding and loading the Calpoke composition to provide energy sources described above.

The size reduction was achieved by first drying the calcium perchlorate in vacuum and then putting it through a Mikro Pulverizer in a dry nitrogen atmosphere. This technique produced calcium perchlorate in 35 micron or smaller particles. The aluminum powder was purchased from Cole and De Graf Co. and was designated 333 wa. This material is a common paint pigment and is leaf-like in shape, rather than spherical or needle-like. The largest dimension of the leaves was about 100 1. Larger or smaller sizes may be used. This material was used after 7,14. spherical aluminum particles were found to produce an over-sensitive material. The PETN was recrystallized from acetone-water mixture to form small crystals and passed through a 100 mesh screen.

The three ingredients were weighted in a dry box under tions produced with different conditions in tests.

To obtain a visualization of models which might be used, e.g., a scale model of the typical reactor above was provided with a 4'' LD. seamless steel tube wall of 0.120" wall thickness with a /8" thick 4" diameter bottom and a /2" thick steel cap bolted on. A /2" high collar was welded about the upper end of the tube for strength. Other scale models in and scales and a wide variety of experiments beyond the scope of the present disclosure were performed using such models.

While there has been described in the foregoing what may be considered to be preferred embodiments of the invention modifications may be made therein without departing from the teachings and scope of the invention and it is intended to cover all such as fall within the scope of the appended claims.

What is claimed is:

1. A minimal gas producing low detonation rate explosive composition comprising a minor proportion of a high explosive in intimate admixture with a greater proportion of a perchlorate of a metal having a valency of at least two and which produces a chloride having a low vapor pressure at the explosion temperature, and a major proportion of particulate aluminum metal.

2. A low detonation rate minimal gas producing explosive composition comprising high explosive in an amount in the range of about 10 to 30% by weight, about 15 to 35 by weight of a perchlorate of a metal being divalent at least and which produces a chloride reaction product having a low vapor pressure at the explosion temperature, and about 40 to 60% by weight of aluminum, said high explosive, perchlorate and aluminum being in a uniform finely-divided intimate composite admixture.

3. An explosive composition as defined in claim 2 wherein said high explosive is a material selected from the group consisting of PETN, HMX, RDX and tetryl.

4. An explosive composition as defined in claim 2 wherein said perchlorate is a metal selected from the group consisting of calcium, magnesium and barium.

5. An explosive composition as defined in claim 2 wherein said aluminum is in the form of leaf-like particles.

6. A low detonation rate minimal gas producing explosive composition comprising a high explosive selected from the group consisting of PETN, HMX, RDX and tetryl in an amount in the range of about 10 to 30% by weight, a perchlorate of an alkaline earth metal selected from the group consisting of calcium, magnesium and barium in an amount in the range of about 15 to 35% by weight, and leaf-like aluminum powder in an amount in the range of about 40 to 60% by weight, said high explosive being in a uniform finely-divided intimate composite admixture.

7. A composition as defined in claim 6 wherein said aluminum powder has a major diameter dimension of the of 100 microns.

8. A low detonation rate minimal gas producing explosive composition comprising a high explosive selected from the group consisting of PETN, HMX, RDX and tetryl in an amount in the range of about 10 to 30% by weight, calcium perchlorate in an amount in the range of about 15 to 3'5 by weight, and leaf-like aluminum powder in the range of about 40 to 60% by weight, said high explosive, perchlorate and aluminum powder being in a uniform finely-divided intimate composite admixture.

9. A composition as defined in claim 8 wherein said high explosive is PETN.

10. A low detonation rate minimal gas producing explosive comprising about 10 to 30% by weight of PETN, about 15-35% by weight of calcium perchlorate and 40- 60% by weight of finely-divided leaf-like aluminum metal particles, said PETN, calcium perchlorate and aluminum metal particles being in a uniform intimate composite admixture.

11. A low detonation rate minimal gas producing explosive comprising about 10 to 30% by weight of PETN, about l35% by weight of calcium perchlorate and 40- 60% by weight of finely-divided leaf-like aluminum metal particles, said PETN, calcium perchlorate and aluminum metal particles being in a uniform intimate composite admixture.

12. A source for producing relatively long duration explosive events with minimal gas production comprising an elongated tubular closed casing member, a compacted intimate admixed composite explosive including a high explosive in an amount in the range of about 10 to 30% by weight, about 15 to 35% by weight of a perchlorate of a metal ion of at least divalency and productive of a chloride reaction product of said metal having a low vapor pressure, and about 40 to by weight of finelydivided leaf-like particles of aluminum metal disposed in said casing, and detonator means disposed in contact with said explosive in said casing.

13. A source for producing relatively long duration explosive events with minimal gas production comprising an elongated tubular closed casing member, a compacted intimate admixed composite explosive including a high explosive selected from the group consisting of PETN, HMX, RDX and tetryl in an amount in the range of about 10 to 30% by weight, about 15 to 35% by weight of a perchlorate of a metal ion of at least divalency and productive of a chloride reaction product of said metal having a low vapor pressure, about 40 to 60% by weight of finely-divided leaf-like particles of aluminum metal disposed in said casing, and detonator means disposed in contact with said explosive in said casing.

14. A source for producing relatively long duration explosive events with minimal gas production comprising an elongated tubular closed casing member, a compacted intimate admixed composite explosive including a high explosive in an amount in the range of about 10 to 30% by weight, about 15 to 35 by weight of a perchlorate of a metal selected from the group consisting of calcium, magnesium and barium and productive of a chloride reaction product of said metal having a low vapor pressure, and about 40 to 60% by weight of finely-divided leaf-like particles of aluminum metal disposed in said casing and detonator means disposed in contact with said explosive in said casing.

15. A source for producing relatively long duration explosive events with minimal gas production comprising an elongated tubular casing member, a compacted intimate composite admixture of PETN in an amount in the range of about 10 to 30% by weight, about 15 to 30% by weight of calcium perchlorate, and about 40 to 50% by weight of aluminum powder of leaf-like particulate form, disposed in said casing, means for closing said casing, and detonator means disposed in contact with said explosive.

16. A source as defined in claim 15 wherein said PETN is present in the amount of about 20% by weight, said calcium perchlorate in an amount of about 25% by weight and said aluminum particles in an amount of about 55% by weight.

No references cited.

BENJAMIN R. PADGETT, Primary Examiner. 

13. A SOURCE FOR PRODUCING RELATIVELY LONG DURATION EXPLOSIVE EVENTS WITH MINIMAL GAS PRODUCTION COMPRISING AN ELONGATED TUBULAR CLOSED CASING MEMBER, A COMPACTED 